Radiation therapy (RT) is a popular and efficient method for cancer treatment, where ionizing radiation is used in an attempt to destroy malignant tumor cells or to slow down their growth. RT is often combined with surgery, chemotherapy, or hormone therapy, but may also be used as a primary therapy mode. Radiation therapy may be administered as internal RT, brachytherapy or, more commonly, external beam RT.
External beam RT typically involves directing beams of radiated particles produced by sources located externally with respect to the patient or subject to the afflicted treatment area. The beam can consist of photons, electrons, protons or other heavy ions. Malignant cells are damaged by the ionizing radiation used during the RT. However, the damage from the radiation is not limited to malignant cells and thus, the dosage of radiation to healthy tissues outside the treatment volume is ideally minimized to avoid being collaterally damaged.
Proton therapy is one type of external beam radiation therapy, and is characterized for using a beam of protons to irradiate diseased tissue. The chief advantage of proton therapy over other particle-based therapies is the ability to more precisely localize the radiation dosage when compared with other types of external beam radiotherapy. During proton therapy treatment, a particle accelerator, such as a cyclotron, is used to generate a beam of protons which is subsequently directed at a tumor or target region. As the beam travels through matter (e.g., the subject), energy from the ionizing radiation is deposited along the path in the surrounding matter. This energy is known as “dose,” and is used to measure the efficacy and accuracy of a radiation beam. Conventional particle accelerators used for proton therapy typically produce protons with energies in the range of 70 to 250 MeV (Mega-electron Volts: million electron Volts). As with other radiation therapies, the charged particles in proton therapy damage the DNA of cells, ultimately causing their death or interfering with their ability to reproduce. Cancerous cells, because of their high rate of division and their reduced ability to repair damaged DNA, are particularly vulnerable to attack on their DNA.
Due to their relatively large mass, proton beams typically will have commensurately less lateral side scatter in the tissue. All protons of a given energy will operate according to a certain range; and relatively few protons will travel (i.e., penetrate) beyond that distance. In addition, the radiation dose delivered to the tissue at a proton beam's target is at its apex during the last few millimeters of the particle's range—this maximum is referred to as the Bragg peak. To treat tumors at greater depths, the proton accelerator must produce a beam with higher energy, typically represented in electron volts (eV). Tumors closer to the surface of the body are treated using protons with lower energy. Thus, damage from the proton beam may be localized to malignant cells by adjusting the energy of the protons during application of treatment.
The purpose of traditional RT treatment planning methodologies is to devise a treatment regimen which produces as uniform a dose distribution as possible to the target volumes whilst minimizing the dosage outside this volume. It is crucial to successful radiation therapy that the discrepancies between dose distributions calculated at the treatment planning stage and those delivered to the patient are minimized. Moreover, just as calculating precise levels of radiation at the treatment planning stage is of great importance, naturally, so is the success of the application of radiation treatments according to the treatment plans. Discrepancies between planned treatment dosages and actually administered treatment dosages can lead to unexpected and potentially disastrous results. Accordingly, proper calibration and (ideally daily) maintenance and quality assurance of the treatment environment, and of the generated radiation beam itself is extremely vital.
Conventional maintenance or quality assurance procedures often include tests to determine a proton beam's range, and constancy. A typical range test may comprise, for example, directing a proton beam according to a treatment plan into an artificial target known as a phantom. Typically, these phantoms are implemented as plastic or glass tanks containing water with submerged or partially submerged radiation measurement devices. The phantom is mounted in one or more positions which occupy the iso-center(s) of the proton beam according to a radiation treatment plan. A proton beam is generated in a particle accelerator according to the pre-determined treatment plan and received in the radiation measurement devices which is scanned while receiving the proton beam to record the beam's characteristics (e.g., energy). Once the beam's characteristics are recorded, the beam may be calculated and compared to the treatment plan to determine congruency or a lack thereof. The proton beam generator may be subsequently re-calibrated to eliminate or mitigate any identified discrepancies between the planned beam and the actual tested beam.
Unfortunately, conventional range determination procedures may require liquid-state phantoms to be quite large. Naturally, due to the volume of liquid required, the phantoms (particularly when filled) may be cumbersome, heavy and/or physically difficult to move and adjust, often requiring two or more operators just to setup the procedure. In addition, such maintenance procedures may require significant time to refill and drain each phantom before and after use. Since these procedures must (ideally) be performed prior to the actual application of radiation treatment, in circumstances where treatments are administered with great frequency, the additional time, effort and personnel required to even attempt to perform such maintenance procedures can become quite prohibitive to conduct efficiently.
Another procedure commonly performed during daily clinical maintenance and quality assurance tests include constancy tests which measure the flux of a field of radiation generated by a proton beam. A typical constancy check includes measuring the field of radiation for a plurality of data points using a device with high spatial resolution, such as a film. However, using a medium or device having a high spatial resolution requires processing for each data point. For devices with high spatial resolution, this can be an extremely time intensive practice, especially when coupled with the performance of inefficient range detection procedures. Moreover, a single layer of film is not reusable, and repositioning multiple layers of film can be time-consuming, especially for frequent or daily tests.